This invention relates generally to the preparation of alpha-olefin oligomers which are useful as synthetic lubricants and functional fluids and more particularly to a BF.sub.3 -promoter catalyst system using alcohol alkoxylates as promoters to control the oligomer product distribution and especially to provide higher percentages of lower oligomers.
Alpha-olefin oligomers and their use as synthetic lubricants ("synlubes") are well-known. The oligomers are usually hydrogenated in order to improve their stability. Early reports of such synlubes are in Seger et al. U.S. Pat. No. 2,500,161 and Garwood U.S. Pat. No. 2,500,163. U.S. Pat. No. 2,766,312 describes the oligomerization of .alpha.-olefins in a Group IV metal oxide bed using a BF.sub.3 -polar promoter catalyst. Promoters include water, carboxylic acid, alkyl halides, alcohols and ethers. U.S. Pat. No. 2,806,072 discloses the dimerization of C.sub.6 -C.sub.12 polypropylenes using a preformed BF.sub.3 -dialkylether catalyst. U.S. Pat. No. 3,882,291 describes the oligomerization of olefins using BF.sub.3 -promoter catalyst complexes which include acid anhydrides, esters, ketones and aldehydes. U.S. Pat. No. 4,172,855 describes BF.sub.3 -promoter catalysts for grafting a second .alpha.-olefin onto C.sub.6 -C.sub.12 .alpha.-olefin dimer to form a low volatility lubricating oil. The promoters include glycol ethers such as ethylene glycol monomethyl ether, propylene glycol monoethyl ether, and di-isobutyl ether.
The particular applications for which the oligomer oils are used depends upon their viscosity, with viscosities of about 2-10 cSt at 100.degree. C. being preferred for general lubricating oil applications. These materials are mixtures of different percentages of dimer, trimer, tetramer, pentamer and higher oligomers which oligomers are produced in different proportions in the oligomerization process. In order to increase the viscosity, processes are used which either produce more of the higher oligomers or some of the lower oligomers are removed such as by distillation. Most low viscosity dimer and trimer products are obtained as by-products of the production of higher viscosity synthetic oils. Due to the increasing use of dimers in applications such as low temperature lubricants and drilling fluids, methods for their preferential production are of interest. It is known that higher temperatures favor dimer production, but such higher temperatures can cause corrosion of production equipment. I have now discovered a new process for producing dimers as the primary oligomerization product at moderate temperatures.